Multifunctional carbon nanotube (CNT) composite fibers are currently of considerable interest in applications where actuation and energy-storage functions are highly desirable, such as electronic textiles. CNT fibers have been shown to function as excellent electrochemical supercapacitors giving specific capacitances of 100 F g -1 [1] . CNT assemblies can also produce useful actuation strains when electrochemically charged [2] and can potentially operate to high stresses because of the excellent mechanical properties of individual CNTs. The development of CNT fibers that simultaneously produce a high capacitance and useful actuation performance remains a challenge however, because the high surface area needed for high capacitance significantly reduces the strength and compromises actuation performance. To date, it has not been possible to develop an ion-conducting binder that mechanically stabilizes the CNT assembly, maintains electrical connectivity between nanotubes, and allows free transport of ions between the nanotubes and an external electrolyte. Pioneering work by Poulin [3] and Baughman [4] have established processing methods for preparing continuous fibers of CNTs and CNT composites that are ideal for electronic textiles. Various studies on these fibers and other CNT assemblies have highlighted the difficulties involved in producing mechanically robust, high-conductivity and high-surface-area electrodes. While single wall carbon nanotube (SWNT) fibers containing ∼40 % poly(vinyl alcohol) (PVA) binder give exceptional mechanical properties, their conductivity is very low at 0.2 S cm -1 .[1] The binder can be removed by pyrolysis to improve conductivity so that the fibers can be operated as electromechancial actuators. While quite high actuation stresses were obtained in these thermally annealed CNT fibers, their low flexibility and high creep during charge and discharge were noted as significant problems.[5] Similarly, fibers spun without the aid of a polymer binder [1] produce high conductivities (140 S cm -1 after thermal annealing) and capacitances (100 F g -1 ) but are mechanically fragile. To resolve these problems, crosslinked DNA has been chosen as a binder for CNT fibers. DNA is a good candidate for improved electrical conductivity for electrochemical devices with CNTs, as DNA has electrical characteristics similar to those of semiconducting diodes in that current flows in one direction only. [6][7][8] In addition, DNA more effectively coats, separates, and solubilizes CNTs than other surfactants because of the large surface area of its phosphate backbone, which interacts with water, and there are many bases in DNA that can bind to CNTs.[9] Therefore, DNA wrapping can debundle CNTs in high concentration CNT dispersions. Consequently, DNA wrapping may improve electrochemical actuation and capacitance of nanotubes in composite fibers by its improved electrical conductivity, high CNT surface area and enhanced mechanical stability due to the p-p interaction between the DNA and the CNT sidewall. We rep...

ABSTRACT:Interpenetrating polymer networks (IPNs) composed of hyaluronic acid and poly(vinyl alcohol) hydrogels were prepared, and the influence of water and the drying kinetics were investigated. The IPN hydrogels were characterized with thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The glass-transition temperatures of the IPN hydrogels decreased with increasing water content. The bound water was the sum of the nonfreezing bound water and freezing bound water. From the DSC melting curves, the values of the total water and freezing bound water were evaluated for IPN hydrogels containing large amounts of water. At the same time, the bound water value was estimated with TGA. In the TGA curves, one-step and two-step weight losses, corresponding to free water and nonfreezing bound water, were observed. The bound water of the hydrophilic polymers broke the hydrogen bonding between the hydroxyl groups of the polymers. The swollen IPN hydrogels exhibited relatively high bound water contents (43.04 -59.17%) by DSC and TGA. The bound water contents of the dry IPN hydrogel films were 10.2-15.29% by TGA. The drying reaction rate constant of the IPN hydrogel increased with increasing temperature.

The swelling behavior of chitosan hydrogels in ionic liquid-water binary systems was studied using hydrophilic room-temperature ionic liquids (RTILs) to elucidate the swelling mechanism of chitosan hydrogels. No penetration of RTIL into a dry chitosan material was observed. Swelling was achieved by soaking in water-RTIL binary mixtures, with larger swelling observed at higher water contents. In one instance, the binary mixture was acidic and produced larger than expected swelling due to the dissociation of the amine groups in the chitosan. The equilibrium binary system content behavior of the chitosan hydrogels depended upon the amount of free water, which is a measure of the number of water molecules that do not interact with the ionic liquid. After evaporation of water, remnant RTIL remained in the chitosan network and hardness testing indicated a plasticization effect, suggesting that the RTIL molecularly mixed with the chitosan. Chitosan hydrogels containing only RTIL were prepared by dropping pure RTIL onto a fully preswollen hydrogel followed by water evaporation. This method may be a useful means for preparing air-stable swollen chitosan gels.